Raspberry-like Nanoheterostructures Comprising Glutathione-Capped Gold Nanoclusters Grown on the Lanthanide...

Bare lanthanide-doped nanoparticles (LnNPs), in particular, NaYF₄:Yb³⁺,Tm³⁺ NPs (UC_Tm), have been seeded in situ with gold cations to be used in the subsequent growth of gold nanoclusters (AuNCs) in the presence of glutathione (GSH) to obtain a novel UC_Tm@AuNC nanoheterostructure (NHS) with a raspberry-like morphology. UC_Tm@AuNC displays unique optical properties (multiple absorption and emission wavelengths). Specifically, upon 350 nm excitation, it exhibits AuNC photoluminescence (PL) (500-1200 nm, λ_max 650 nm) and Yb emission (λ_max 980 nm); this is the first example of Yb sensitization in a UC_Tm@AuNC NHS. Moreover, under 980 nm excitation, it displays (i) upconverting PL of the UC_Tm (at the blue, red and NIR-I, ca. 800 nm, regions); (ii) two-photon PL of AuNC; and (iii) down-shifting PL of thulium (around 1470 nm). The occurrence of energy transfer from UC_Tm to AuNCs in the UC_Tm@AuNC NHS was evidenced by the drastic lengthening of the AuNC PL lifetime (τ_PL) (from few hundred nanoseconds to more than one hundred microseconds). Initial biological assessment of UC_Tm@AuNC NHSs in vitro revealed high biocompatibility and bioimaging capabilities upon near-infrared excitation.